In the field of wireless mobile communication, techniques have been proposed to compensate non-linear distortions of a power amplifier used at a base station or the like. According to one of the techniques, when signals in a plurality of frequency bands are concurrently amplified by a power amplifier used in common, non-linear distortions are compensated by using a plurality of distortion compensation units or a dual-band Digital Pre-Distortion (DPD) method. Further, known examples of a power amplifier employing the dual-band DPD method include a power amplifier having a Volterra filter of a dual-input truncated Volterra model provided at a stage preceding a two-dimensional Look-Up Table (LUT) so as to also compensate second order distortions. Other examples include a method configured to compensate harmonics or intermodulation distortions occurring in another band by inputting a signal having an inverse characteristic to a power amplifier and a method configured to compensate distortions by solving non-linear simultaneous equations.    Patent Document 1: Japanese Laid-open Patent Publication No. 2002-084146    Patent Document 2: Japanese Laid-open Patent Publication No. 2012-227881    Patent Document 3: Japanese Laid-open Patent Publication No. 2014-003527